The present invention relates to a method and an apparatus for continuously soldering the abutting ends of links of chains of precious metals or chains plated with precious metals which may be manufactured by automatic soldering.
When manufacturing chains of precious metals open links with joint places abutting ends are formed, which have to be soldered together in order to increase the tensile strength of the chain. In prior known methods the chain which has not yet been soldered together used to be dipped into or drawn through a semi-liquid or powdered solder, whereupon the solder is removed from all parts except in the abutting ends. Generally the chain is then covered with a thin layer of talcum. The chain thus prepared for being soldered is thereupon moved across a heating device hanging in the vertical direction, which heating device is generally a gas heated closed box in which the chain is heated to such temperature that the solder melts and the abutting ends are soldered together.
In other cases the chain can be made of a thin tube of metal whereby solder and sometimes also fluxing material is applied in the interior of the said tube. Also in this case the soldering of the abutting ends is made in that the chain is brought to pass a heating device, whereby the solder melts and the joint ends are soldered together.
This prior known method however involves some disadvantages. When heating the chain the metal softens, especially in case of chains of silver, and it may happen that the abutting ends, depending on the weight of the chain itself and the reduced stiffness of the material caused by the heat open somewhat so that the solder does no longer fill the space between the abutting ends. Thereby an unsoldered link is obtained in the chain, which link is difficult to detect and which is an obvious risk in the rupture of the soldered chain.
In some cases there can be excess of solder in the abutting ends, and a part of the solder can flow out of the abutting ends during the soldering. Since the links hang in each other during the soldering the solder flowing out of the abutting ends may depending on the capillary forces be sucked into the area between two links so that the said links are soldered to each other.
Attempts have been made to eliminate the disadvantage that the abutting link ends open by mixing alloys into the chain metal, generally some heavy metal as e.g. cadmium which reduce the tendency of the link to open when being heated. The heavy metals however give toxic fumes which cause problems for the persons handling the metal. Attempts have also been made to eliminate the disadvantage of the above mentioned soldering of links by isolating the chain with a layer of talcum as mentioned above. Such isolation however gives a very limited protection against such soldering especially since the talcum easily loosens from the chain before and during the soldering.